1. Field of Invention
This invention relates to orifice pulse tube refrigerators and, in particular, to orifice pulse tube refrigerators that employ a vortex tube as the heat-rejecting heat exchanger at the warm end of the pulse tube.
2. Description of Prior Art
In the prior art double inlet arrangement for an orifice pulse tube refrigerator, a compressor is connected to the refrigerator in two places. One connection, through which flow is unrestricted, cyclically forces fluid into and withdraws fluid out of the regenerator, as shown in FIG. 1. The other connection, the xe2x80x9cdouble inlet passagexe2x80x9d, is a restricted channel through which the compressor cyclically forces and withdraws a limited quantity of fluid. Heat exchangers and a pulse tube complete a loop between the two points at which the compressor is connected to the refrigerator.
The double inlet passage is connected to the warm end of the prior art pulse tube between the warm heat exchanger and the orifice that connects the warm heat exchanger to a reservoir. Fluidic devices in the double inlet passage connecting the compressor to the warm end of the pulse tube have been employed to control the direct current flow (hereinafter xe2x80x9cDC flowxe2x80x9d) that would otherwise occur when the compressor is connected to the pulse tube at both ends through two separate passages. Experience has shown that some DC flow may be desirable under some conditions. A fluidic device such as a vortex diode, directional jet, or Tesla diode can bias the flow in the double inlet passage so that optimal net DC flow can be obtained as fluid passes back and forth between the compressor and pulse tube.
The purpose of incorporating a double inlet passage at the warm end of an orifice pulse tube refrigerator is to alter the phase of flows in the cold end of the pulse tube relative to pressure. Bleeding some fluid through the double inlet passage to the warm end of the pulse tube as pressure is rising tends to retard the entrance of fluid from the cold heat exchanger into the pulse tube until pressure is high. Then, when fluid emerges from the cold heat exchanger into the pulse tube, it is not adiabatically heated as the pressure rises. It can then be adiabatically cooled, as pressure falls, to a lower temperature than could be obtained if the fluid had first been heated to a higher temperature in the pulse tube.
As pressure is falling, the double inlet bleeds some fluid from the warm end of the pulse tube, retarding the flow of cold fluid back into the cold heat exchanger, and permitting the fluid to cool adiabatically for a longer time, and to a lower temperature, than would otherwise be possible, before passing through the cold heat exchanger.
The amount of fluid that flows back and forth in the pulse tube of a pulse tube refrigerator is limited by the volume of the pulse tube. That is, some fluid must remain in the pulse tube at all times. While some fluid moves back and forth between the cold end of the pulse tube and the cold heat exchanger and some fluid moves back and forth between the warm end of the pulse tube and the warm heat exchanger, a substantial quantity of fluid in the middle of the pulse tube must simply move back and forth in the pulse tube. As a consequence, the volume of fluid that passes from the warm end of the pulse tube to the reservoir and back again must be limited to a fraction of the volume of the pulse tube, of the order of ⅓ of that volume, or less. The flow back and forth in the double inlet passage is typically smaller than the flow between pulse tube and reservoir.
The concept of a xe2x80x9cblindxe2x80x9d vortex tube as heat-rejecting heat exchanger at the warm end of a pulse tube refrigerator has been patented (U.S. Pat. No. 6,109,041), incorporated herein by reference, as have a variety of related vortex devices (U.S. Pat. No. 5,966,942), also incorporated herein by reference. However, none of those vortex devices has connected the warm end of a vortex tube to the compressor of an orifice pulse tube refrigerator through a channel that bypasses the regenerator. None of those prior art vortex devices has described a double inlet passage of any kind.
Although prior art vortex devices have advantages as heat-rejecting heat exchangers at the warm end of a pulse tube refrigerator, all such devices heretofore proposed have been subject to the same flow limitations as conventional heat exchangers employed at the warm end of a pulse tube, thereby limiting their effectiveness.
In accordance with the present invention, an orifice pulse tube refrigerator comprises a compressor, regenerator, cold heat exchanger, pulse tube, cold throat, vortex tube, vortex generator, reservoir connected to the vortex tube through the vortex generator, double-inlet passage connected between the remote end of the vortex tube and the compressor and means for controlling DC flow through the double-inlet passage. In operation, fluid flows into and out of the vortex tube through the small end of a cold throat, through a vortex generator located between vortex tube and reservoir, and through a double inlet passage that connects the remote end of the vortex tube to the compressor through diode.
Thus, all passages between the vortex tube and the other volumes to which it is connected are restricted. Flows through the three passages are controlled by the restrictive components peculiar to their location, but flows through each such restrictive component are also affected by the flows permitted by the other components. Thus, the flow back and forth through the cold throat is affected by the size of the cold throat opening, but also by the momentary differences between pressure in the pulse tube and pressure in the vortex tube.
The momentary pressure in the vortex tube is, in turn, affected by flows of fluid back and forth through the double inlet passage and flows to and from the reservoir. The limitation on flows back and forth through the cold throat remains; no more than a fraction of the fluid in the pulse tube may be permitted to pass back and forth through the cold throat. However, no such limitation is imposed upon the flows back and forth through the double inlet passage, or through the vortex generator. Thus, the combined flow from the pulse tube and the double inlet passage through the vortex tube and vortex generator to the reservoir may exceed the total volume of the pulse tube. That is not achievable with prior art orifice pulse tube refrigerators. With such relatively large flows back and forth through the vortex generator, the vortex tube is particularly effective, since much of the heat developed in the vortex tube can be rejected back to the compressor through the double inlet passage. Rejection of heat at the warm end of the pulse tube, in turn, is the basis of the cooling effect at the cold end of the pulse tube.
To achieve that effect, all openings to the vortex tube are calibrated relative to each other so as to permit optimum fluid flows through the cold throat relative to the volume of the pulse tube, optimum flows between the remote end of the vortex tube (where the double inlet passage is connected) to the reservoir, and optimum DC flow through the double inlet passage. When those adjustments have been made, the vortex tube functions as a more effective warm heat exchanger than any prior art alternative because it returns fluid through the cold throat to the pulse tube at a lower temperature than can be achieved by any other means.
Accordingly, besides the objects and advantages of orifice pulse tube refrigerators in general and orifice pulse tube refrigerators equipped with vortex devices as warm heat exchangers, several objects and advantages of the present invention are:
(a) to provide a heat-rejecting heat exchanger with superior heat-rejecting capacity;
(b) to provide a heat rejecting heat exchanger that is easily fabricated at low cost;
(c) to provide a heat-rejecting heat exchanger that allows optimum adjustment of flows through a double inlet passage;
(d) to provide a double inlet arrangement that removes larger amounts of heat from the heat-rejecting heat exchanger than would otherwise be possible;
(e) to provide an orifice pulse tube refrigerator with a heat-rejecting heat exchanger that is simple, sturdy and reliable;
(f) to provide a vortex tube heat rejecting heat exchanger that can receive, and reject heat from, a volume of fluid greater than that which can be permitted to move into and out of the pulse tube of an orifice pulse tube refrigerator.